Manufacture of Biodiesel

ABSTRACT

A continuous manufacturing process is described. Vegetable oil is reacted with methanol and a catalyst such as KOH to produce biodiesel and glycerol. The reactants are passed through a reaction zone with magnetostrictive components ( 4 ) in it while subjecting them to a strong alternating rotatory magnetic field, preferably adjusted to produce a resonant acoustic or ultrasonic field in the reaction zone.

This invention relates to the manufacture of biodiesel, i.e. themanufacture of fuel which can be used to power conventional dieselengines but which is derived not by petrochemical processing steps fromcrude oil, but rather from biologically produced materials, most notablyvegetable oils.

The basic method of manufacturing biodiesel is well-established andindeed has been commercialised in a number of countries. It consists intaking vegetable oil and methanol and reacting them together in thepresence of a catalyst. A transesterification process takes place givingas the reaction product a mixture of fatty acid methyl esters (FAME,which is the biodiesel itself) and glycerol. In the case of the use ofrape oil as starting material, the biodiesel product is often referredto as rape methyl esters (RME).

Commercial manufacture as practised consists in combining the vegetableoil with methanol in a reaction vessel in the presence of a catalystsuch as sodium or potassium hydroxide or sulphuric acid. Thetransesterification reaction strips the fatty acids from the glycerolbackbone of the vegetable oil molecules and attaches methanol moleculesto them. Extra methanol is put into the reaction cylinder to increasethe output of e.g. RME and, following the end of the reaction, themixture of biodiesel, glycerol and excess methanol, the catalyst andsundry impurities is then removed from the vessel and separated, themethanol and catalyst usually being recycled into the process, and thebiodiesel sold as such. The glycerol is a valuable by-product which canbe used in various manufacturing processes.

It is well-established that the current methods of manufacturingbiodiesel on a commercial scale are not particularly efficient. Inparticular, the reaction time for the mixture is substantial, usually1.5 to 10 hours, and power consumption is around 40 Kw so the totalenergy needed to make the biodiesel is very substantial. Proposals havebeen made to reduce the reaction time, particularly by adopting acontinuous rather than batch approach and pumping the oil and methanolmixed with the catalyst through a reactor chamber at high pressure, forexample 80 to 100 Bar. The pressure is required because, operating inthis way, as the mixture is passed through a reactor vessel includingstatic reactor elements, there is intimate phase mixing which gives avery high mass transfer between the reactants. The engineeringrequirements of operating at such high pressures are, however,challenging and the energy consumption correspondingly high.

We have now discovered that the transesterification reaction is drivento completion very much faster by carrying it out in a reactor vesselwhere the reaction chamber area is subjected to high alternating rotaryelectromagnetic fields and, in addition to the reactants identifiedabove, the reactor vessel includes a large number of magnetostrictivecomponents.

Operating in this way, a transesterification reaction can be carried outat normal temperature and normal pressure very rapidly, and the excessof methanol needed in traditional operation is unnecessary.

According to the present invention therefore there is provided a methodfor the continuous manufacture of biodiesel which comprises reactingvegetable oil and methanol in the presence of a catalyst to producebiodiesel and glycerol, wherein the reaction takes place in a reactionzone in which magnetostrictive components are present in the mixture ofreactants and the zone is subjected to a strong alternating rotatorymagnetic field. The rotation of the magnetic field is preferably atleast 3000 rpm. Preferably also the magnetostrictive components areexcited by the primary magnetic field to generate a resonant acoustic orultrasonic field within the chamber. The production of such a resonantfield may be assisted by dividing the chamber into sections e.g. by theuse of a plurality of perforated baffles or the like through which themixture of reactants may pass, and the spacing of which is chosen tomatch the desired resonance.

The precise mechanism by which the reaction speed is materiallyaccelerated is understood now in general outline. It is undoubtedlyrelated to the magnetically generated effects mediated by the individualmagnetostrictive pieces of material. These may be particles or, forexample, small cylindrical iron bodies. For reasons of economy,iron-based materials are preferred, but ferrous alloys, particularlyones including lanthanides such as dysprosium or terbium may provideenhanced results, as may mixed materials such as alfer. If desired,non-ferrous ferromagnetic elements or alloys may be used.

In the active centre of the reaction zone, high intensive physicalfields of different nature are generated, such as electromagnetic,mechanical, acoustical and inertonic. Their specific power is verysignificant and when they influence species of the substance underconsideration, they ensure deep structural and energetic changesincluding changes in the valence electronic shells of atoms. In ourapparatus the electromagnetic field is generated in such a way that inthe reaction zone the configuration of the field becomes so effectivethat the magnetic agents are in a resonant condition, which allows us tomaximise the effects of magnetostrictive agents. The resonant effectsallow the control of turbulence and hence the agents move along specialtrajectories, such that they do not practically collide, which preservetheir destruction. These effects can be enhanced by the inclusion ofresonance sub-chambers in the reaction vessel. The total influence ofthese factors results in deep excitation over the whole of thecross-section of the reactor and in a strong degree of activation of allcomponents of the substance which participate in the process of thetransesterification reactions. This yields significant increases of thesurface of interaction or interface of the process.

A very quick intermixing, decomposition and, which is most important,activation of substances in the active centre of the reactor chambermakes it possible to realise physical-chemical processes at a rate thatsignificantly exceeds that achieved in conventional chemical-physicalprocesses. In other words, this allows one to pass from diffusive tokinetic reactions.

The improvement in reaction rate is generally dependent upon thestrength of the primary magnetic field and the frequency of itsoscillation, and on the mass and dimensions of the magnetostrictivecomponents activated by the magnetic field. In practical terms, however,there is a trade-off between the cost of generating the electromagneticfield and the economic benefits of the faster reaction.

The use of ferromagnetic particles subjected to a rotating magneticfield and being suspended in a liquid has been previously proposed, see“Intensification of technological processes in apparatus with vortexbands”, D D Logvinenko and O P Shelyakov, Technika, Kyiv 1976 and U.S.Pat. Nos. 3,969,129, 4,093,189, 3,869,251 and 3,691,130 for variousaspects of this. None of these publications discloses the value of thetechnique in biodiesel or similar manufacture, or the use of a resonanceeffect in the reaction vessel, which is found under the influence of theprimary non-stationary electromagnetic field, to improve reaction rates.The resonance is produced by means of a special winding for each of thethree phases of the reactor. Each phase is fed through a parallelresonant circuit, such that the resonant frequency is within thekilo-Hertz region.

We have found that this can be achieved by winding the coils whichproduce the rotatory magnetic field in a way which is very differentfrom the conventional approach to winding coils e.g. in an electricmotor or generator, and by driving them electrically with differentphase shifts, frequencies and amplitudes. Preferred arrangements whichmay be driven by power suitably modified from that provided by astandard three-phase mains supply include three sets each of twowindings, each set being supplied with current derived from each phaseof the supply. The coils are not driven in a synchronous manner, and actto produce a controlled chaotic action in the magnetostrictiveparticles, which individually resonate at high frequency if the drivesto the coils are appropriately tuned.

The plant or apparatus used to carry out the process of the presentinvention may vary in scale, depending on the desired throughput incontinuous operation. These are described with reference to theaccompanying drawings in which:

FIG. 1 shows, diagrammatically, a central reactor chamber forming partof apparatus for carrying out the invention; and

FIG. 2 is a schematic block diagram of a continuous operation pilotplant for biodiesel production.

Referring to FIG. 1, this shows diagrammatically a core reaction chamberassembly for making biodiesel, together with a power supply, for examplea 3-phase 50 or 60 Hz AC mains supply, denoted 1. This feeds current toa set of coils 2 constituting an electromagnetic field generator. Thecoils 2 are located around a non-magnetic tube 3, e.g. of stainlesssteel. A reactor chamber 5 in the form of a stainless steel cylinder ofcapacity of 1.5 litres is located centrally in pipe 3. Reactant mixturemay be fed into chamber 5 via an inlet pipe 6 and leave via an outlet 7.Inside the chamber 5 are a large number of cylindricalferromagnetic/magnetostrictive components as activating agents. Sincethe chamber 5 is located between the coils 2, when the coils areconnected to a suitable source of oscillating electrical power andcontrolled with a view to providing a rotating magnetic field at thecentre of the reaction chamber 5 of strength 0.10 to 0.15 Tesla, theactivating agents may be vigorously affected. As the power source 1 isthe conventional electric mains, the oscillation frequency is 50 or 60Hertz, and the rotation rate of the field is 3000 or 3600 rpm.

FIG. 2 shows diagrammatically a complete pilot plant for the continuousmanufacture of biodiesel in accordance with the present invention.

Referring to FIG. 2, the actual biodiesel production takes place in areaction chamber generally denoted 10. This is surrounded by coils 36energised by a power supply unit 11.

The raw materials of biodiesel manufacture are kept in appropriatestorage vessels, viz. a waste oil supply tank 12, a methanol tank 13 anda store for potassium hydroxide 14. Methanol hydroxide may be fed bymeans of a pump 16 into a mixer unit 18 where the potassium hydroxide isdissolved. The solution is then passed by a pump 17 via one of a pair ofmetering valves 22 into an emulsifier 24. Separately, oil may be pumpedfrom a holding tank 12 by means of a pump 20 and via a second one of thepair of proportioning valves 22 into an emulsifier unit 24. In theemulsifier unit, the mixture of oil with methanol and potassiumhydroxide is emulsified by means of vigorous mechanical agitation.

The emulsion then flows through the reaction chamber 10. Located insidechamber 10 which is generally cylindrical is an axial threaded rod 30 onto which are threaded four metallic perforated discs 32. The positioningof the discs 32 may be adjusted by turning them on the threaded shaft 30and is adjusted to tune the system so that, during operation, itconstitutes an acoustic resonant cavity. Also located in the reactor 10are ferromagnetic cylinders 34 which can be excited vigorously by meansof the magnetic field generated by coil 36 internally of the reactorchamber 10.

The treated emulsion emerges from an outlet port at the end of thereaction chamber 10 and passes into the holding and settling tank 26.Biodiesel may be withdrawn via a valve 27 located part way up the sideof tank 26 and glycerol via a valve 28 near the bottom.

The following example, which used the apparatus shown in FIG. 2, willserve to illustrate the invention.

EXAMPLE

The feedstock for conversion to biodiesel was rape seed oil. Thedissolution unit 12 was controlled in order to provide an 8% by weightsolution of potassium hydroxide in methanol.

The potassium hydroxide solution in methanol and feed oil were thenemulsified on a continuous basis at a weight ratio of 122 kilograms ofthe potassium hydroxide in methanol solution per 1000 kilograms of therape seed oil.

The flow through the reaction chamber was 5 tonnes per hour of emulsion.During its passage through the reactor chamber, the emulsion wassubjected to intense agitation as a result of the application of therotating magnetic field by means of coils 36. The length of the reactionchamber under the influence of the magnetic field was 670 mm, the innerdiameter of the chamber being 100 mm. The reactor chamber was tuned tooperate as a resonant cavity. The speed of sound in the emulsion beingaround 2000 metres per second, the generation of an acoustic standingwave having a wavelength of around 166 millimetres and a fundamentalfrequency of around 12 KHz was achieved. Measurement showed that therewas a certain amount of 24 KHz and higher harmonics were achieved. Thechamber included, located captive in each of the sections, 600 gm ofmagnetorestrictive components in the form of iron cylinders of length 15mm and diameter 1.0 mm.

The power consumption during continuous operation is around 3 to 4

Kilowatt hours per tonne of biodiesel produced. The amount of methanolin the output is less than one percent by weight. If desired, this mayeasily be removed from the biodiesel by an appropriate rectification ordistillation process and recycled to the methanol storage tank 13.

1. A method for the continuous manufacture of biodiesel which comprisesreacting vegetable oil and methanol in the presence of a catalyst toproduce biodiesel and glycerol, wherein the reaction takes place in areaction zone in which magnetostrictive components are present in themixture of reactants and the zone is subjected to a strong alternatingrotatory magnetic field.
 2. A method according to claim 1 wherein therotation rate of the magnetic field is at least 3000 rpm.
 3. A methodaccording to claim 1 or 2 wherein the individual magnetorestrictivepieces of material are small cylindrical iron bodies.
 4. A methodaccording to any one of claims 1 to 3 wherein the alternating rotarymagnetic field is one which produces acoustic resonance in the activecentre of the reaction zone.
 5. A method according to claim 4 whereinthe reaction zone is divided by a plurality of perforated baffles,spaced to promote the resonance.
 6. A method according to any one ofclaims 1 to 5 wherein the magnetic field strength in the reaction zoneis around 0.1 Tesla.
 7. A method according to any one of claims 1 to 6wherein the catalyst is an alkali metal hydroxide.
 8. A method accordingto claim 7 wherein the alkali metal hydroxide is first dissolved intothe methanol and the solution then mixed with the vegetable oil and themixture thereby formed is emulsified prior to entering the reactionchamber.